This invention relates to a sampling device for use in an automatic chemical analyzer.
Recently, in the field of chemical analysis, due to the large increase in the number of samples being treated, automatic analyzers have come to be widely used. In particular, there is a great demand for automatic analyzers capable of carrying out different kinds of analysis by repeatedly sampling small quantities of sample from the same container or receptacle. However, with this type of automatic analyzer, there is a need for a sampling device capable of measuring out small quantities of sample accurately and of preventing sample contamination due to repeated sampling.
Sample devices according to the prior art can be broadly classified into two types; the valve-cut type and the pipette type. The former type, as shown in FIG. 1, comprises a slide valve consisting of a sliding member 4, equipped with a sample measuring hole 3, sandwiched between two fixed bodies 1 and 2, said fixed bodies 1 and 2 being respectively provided with thru-ways 5 and 6, and 7 and 8 which are respectively connected to feed lines 9 and 10, 11 and 12, said feed lines being, in turn, connected to a sample suction pump 13, a reagent pump 15, a suction pipette 14, a discharge pipe 16 respectively. Operation of the valve-cut type sampler is as follows. First of all, the sliding member 4 moves so that the sample measuring hole 3 aligns with thru-ways 5 and 6. The sample suction pump 13 now commences to operate and a small quantity of sample is sucked up through pipette 14. As a result, thru-way 6 and measuring hole 3 fill up with liquid sample and thru-way 5 becomes partially filled with sample. Next, sliding member 4 moves so that the sample measuring hole 3 aligns with thru-ways 7 and 8. By so doing, the reagent pump 15 comes into operation and the sample, together with the reagent, passes through the discharge pipe 16 and into the reaction tube 18a. When the sample and reagent has entered the reaction tube 18a, the sliding member 4 returns to its original portion; i.e., measuring hole 3 once again aligns with thru-ways 5 and 6, and the suction pipette 14 moves over to a washing beaker 19. When this occurs, the action of the sample suction pump 13 is reversed so that the sample remaining in thru-ways 5 and 6, and feed lines 9 and 10, and any reagent remaining in measuring hole 3 is washed out. When this operation is complete, the pipette 14 moves either back to the sample tube 17a if repeated sampling of the same sample is intended or to another sample tube; e.g., sample tube 17b, if a different sample is to be sampled, and the same process as heretofore described, is repeated.
Although the above described valve-cut type sampling device possesses high reproducibility, it does have a disadvantage in that excess sample; i.e., the sample in thru-ways 5 and 6 which is not used for actual analysis, is sucked up in order to fill measuring hole 3 when the suction pump 13 is operated. And, since the amount of excess sample, as compared with the amount used for actual analysis, is large, sample utilization efficiency is poor which makes this type of sampling device unsuitable for measuring out and sampling minute quantities of sample. In addition to which, when the suction pipette 14 is reinserted into the sample tube after being washed, small drops of water adhering to the pipette are deposited into the liquid sample, thereby causing contamination. If there is only one sampling from each sample tube, this does not present much of a problem but in the case of repeated sampling from the same tube, the problem of contamination becomes consequential.
On the other hand, the latter type of sampling device (viz., the pipette type sampler) is shown in FIG. 2. In FIG. 2a, the sample suction pump 20 and the pipette 21 are connected directly. In this case, a fixed amount of sample is sucked up from the sample tube 22 through a pipette 21 by the action of the sample suction pump 20. The pipette 21 then moves over to the reaction tube 23 and deposits its contents therein. This completed, the pipette moves over to the washing beaker 24 and, after the pipette has been washed, the same process is repeated. In FIG. 2b, the pipette and suction pump are connected through a flow path changeover valve 25. In this case, one of the valve inlets is connected to a reagent pump 26 and a quantity of the sample is sucked up by the suction pump 20. After which, the valve operates so as to change over the sample flow path, the reagent pump then comes into operation and the sample is discharged into the reaction tube 23.
The pipette type of sampling device has an advantage in that structurally it is comparatively simple. However, the problem common to the valve-cut type of sampling device are present. For example, small drops of water remain on the tip of the pipette after washing which contaminate the unsampled sample in the case of repeated sampling. There is also the problem of sample cut-off at the pipette tip which makes precision sampling difficult, especially when dealing with very small quantities of sample.
In a nutshell, sampling devices according to the prior art, regardless of type, are incapable of completely preventing sample contamination if repeated sampling is carried out from the same sample tube or container. Thus, sample reproducibility deteriorates, a factor which becomes very pronounced when the sampling quantity is very small.
One object of the subject invention is to provide a sampling device capable of measuring out small quantities of sample accurately.
Another object of the subject invention is to provide a sampling device capable of measuring out sample under contamination-free conditions, regardless of sampling frequency.
Yet another object of the subject invention is to provide a sample measuring device having a high sample utilization efficiency.
Still another object of the subject invention is to provide a sample measuring device suitable for repeatedly and automatically measuring and sampling.